How Much Of A Health Risk Is Listeria Really?

Last week, Sabra recalled 30,000 cases of its Classic Hummus for possible Listeriamonocytogenes contamination, and Blue Bell recalled more varieties of its ice cream products [Update, 4/21/15: Now it's recalled all of them]. Before that, it was spinach, sprouts, and caramel apples. Though no illnesses have yet been linked to Sabra products (the contamination was found during a random inspection of the product), five illnesses and three deaths have been linked to the Blue Bell contamination, which may date back to 2011. From the consumer’s vantage point, it seems like Listeria contamination in major food brands is on the rise these days. Are the outbreaks actually increasing, or are we just more aware of them? That may not be such an easy question to answer at this juncture, but safety measures in food manufacture will surely be intensified as a result.

Tracking Listeria Proves Tricky

“According to the Center of Disease Control (CDC), there have been eight outbreaks of Listeria since 2011. Five of these outbreaks have occurred since 2014,” says Dr. Ari Grinspan, gastroenterologist at The Mount Sinai Hospital. So it does seem like there's been a bump in recent months. "But the largest outbreak occurred in 2011 when 147 people became sick from Listeria,” adds Grinspan. “This outbreak was associated with cantaloupes from a single farm in Colorado. Thirty-three people died due to Listeria infection and one miscarriage was reported.”

NEW YORK, NY - APRIL 09: Sabra Dipping Co. is recalling 30,000 cases of hummus due to possible contamination with Listeria, the U.S. Food and Drug Administration said Wednesday. (Photo by Spencer Platt/Getty Images)

Listeria is a particularly ugly pathogen since the number of people who die from it relative to the number infected is quite high. From 2011 data, it seems that about 1600 people are infected from listeria each year, and 260 die. In contrast, only about 380 people die from the 1 million cases of Salmonella in the country each year.

But measuring the “behavior” and spread of Listeria is difficult, and subject to some degree of guestimation. Because of overlapping symptoms with other illnesses, it can be hard to know the actual numbers of infections – of Listeria or any other microbe – as it’s difficult to determine how many cases are diagnosed vs. undiagnosed.

“The problem with stats is they use different methods to calculate and it is difficult to compare, says Dr. Philip M. Tierno, Jr, Professor, Microbiology & Pathology at NYU’s School of Medicine and The NYU Langone Medical Center. “The other problem is not all cases are reported or are culture confirmed. Also, for example, it is estimated for every 1 cultured case of toxigenic E. coli there are 26 cases not diagnosed; for Listeria there are 2 cases not diagnosed; for Salmonella there are 29 cases not diagnosed; and so on. So you see the difficulty."

It’s not clear whether the Sabra contamination has or will lead to any illnesses. It can take up to two months for an exposed person to develop symptoms, but no cases have been associated with the hummus recalls so far.

Who Becomes Ill, vs. Critically Ill?

Symptoms of Listeria can range from manageable-at-home to life-threatening. “In otherwise healthy adults,” says Grinspan, "Listeria infection will present with self-limited fever, muscle aches and diarrhea – similar to ‘stomach flu’ symptoms. While pregnant women can develop similar symptoms, the concern is that infection can lead to miscarriage, stillbirth or preterm labor. Older adults and people with weakened immune systems can develop severe symptoms such as meningitis characterized by headache, stiff neck and confusion.”

Again, in many cases, healthy adults are generally not at high risk of becoming seriously ill from Listeria. But pregnant women, infants, elderly people, and those with compromised immune systems (e.g., who are taking immunosuppressant medications, have HIV/AIDS, or are undergoing chemotherapy) are at the greatest risk. People in any of these categories are urged to seek medical care right away if they experience Listeria-like symptoms.

Preventing Future Illnesses

Listeria generally comes from water and soil contamination somehow making its way into food plants. Food safety and hygiene at every step of processing are critical, of course, and steps to enhance prevention will likely be heightened in the coming months.

“Obviously outbreaks get a lot of attention, but Listeria is an extremely common foodborne illness,” says Dr. Jonathan L. Jacobs, Infectious Disease Specialist at NewYork-Presbyterian/Weill Cornell Medical Center. “It is found in many places in nature – water, soil, and animals that are infected without having symptoms. Contamination can come from any of these sources and affect food-processing equipment. Another property of Listeria that makes it such a difficult pathogen is the fact that he can withstand refrigeration temperatures.”

This is part of what makes Listeria hard to track – that it can live in refrigerated products for months, and frozen products for years. The Blue Bell contamination may have started as far back as 2011, but producing problems only now since many of the products are still fresh today. There is a number of food sources that have been linked to Listeria in the past, like soft cheeses, raw milk, smoked seafood, and deli meats, which experts may advise people in the high-risk groups to avoid, if possible.

While the FDA figures out how to step up aseptic practices, there’s unfortunately not a whole lot consumers can do differently, aside from washing fruits and veggies completely and perhaps cooking vegetables like spinach thoroughly. Avoiding the most likely food culprits if you’re pregnant or otherwise at higher risk is probably wise.

“Pregnant women in particular should pay attention to what they eat,” says Jacobs. “Soft cheeses and refrigerated deli meats (even previously thoroughly cooked), and vegetables and fruits that they may not have been thoroughly washed such as bean sprouts and melons have all been implicated in outbreaks….There are so many potential sources that people, especially those at highest risk, should adhere to food safety guidelines as much as they can.”